I prefer the 2" because I feel like there is less pressure per sq. in. Kind of like putting a fishing line around your neck and then trying a 5/8" braided rope and see which feels better. All I know is 2 things: get the collar from Collarmania and the lead from Ella's lead. Mine is great and will buy nothing else. They have a gallery at collarmania to see some on other dogs to give you and idea on different color dogs.

I tend to prefer the 1.5" collars, and since my boy is so lightly built I got him a 1.25". The wider collars do disperse the force over a greater area, but they also are bulkier and I think they seem less comfortable for just wearing around. Like the way I hate wearing wide rings but narrow rings don't bother me. The 1.5" are still plenty wide to make them comfortable on a leash.

Take a sheet of notebook paper (colored would be best, so you can see it) and fold it to two inches. Wrap it around the dogs' necks and take a look. Take another and fold it to 1.5 inches and give that a shot.